Field
The present invention relates to a method for processing or fabricating a scintillator array, and more specifically to a method for fabricating, e.g., a gadolinium oxysulfide (GOS) ceramic scintillator array by using a laser cutting process and a diamond blade cutting process. The GOS scintillator array manufactured by the processing method of the present invention can be used in X-ray or γ-ray ionizing radiation imaging detectors for X-ray computed tomography (X-CT) and/or line-scan imaging, and is especially applicable to the field of radiation imaging security check.
Description of Related Information
A detector used in computed tomography (CT) scan system and line-scan X-ray detection system is constituted by a scintillator, a photodiode coupled with the scintillator, and a back-end electrical signal processing unit. In order to avoid crosstalk of optical signals detected by the photodiodes, the scintillator is usually processed into an array with a size corresponding to the size of a center of the photodiode, and an isolation layer that can reflect visible light is located between pixels of the array. Existing cutting or dividing techniques for scintillator array pixels generally use a circular diamond blade cutting process and/or a diamond wire sawing process. Generally, it is desirable that gaps between the pixels are narrow enough such that an effective volume of the respective pixel can be as large as possible and thereby detective quantum efficiency on ionizing radiation can be improved. However, the gap should not be too narrow. Otherwise, it is difficult to guarantee an enough thickness of the light-reflective material filled in the gap, which may cause incomplete shielding of scintillation (or luminescent) light and optical crosstalk among the pixels. Generally, there are large gaps between the pixels of the scintillator which are cut by the circular diamond blade. This is because the circular diamond blade should have a certain thickness to guarantee enough strength and it is difficult to reduce the blade oscillation resulted from the vibration of the cutting machine during its high-speed rotation to a low enough extent. The diamond wire sawing process can produce small gaps between the pixels of the scintillator. However, the diamond wire saw has a complicated structure, and its processing efficiency is low for small-batch and medium-batch processing. Furthermore, end surfaces produced by grinding of diamond abrasive particles are smooth and coolants used during cutting may remain on the end surfaces of cuts. If the residual coolants have not been thoroughly removed and an optical synthetic-resin cement comprising titanium dioxide light-reflective powder is filled into the narrow gaps, the strength of adhesion between the scintillator pixels and the synthetic-resin cement may not be large enough. Therefore, in this case, it is needed to pay more attention to subsequent coupling operations of the scintillator array in order to avoid fracture at the adhesive gap when the scintillator array is in a stressed state, which would increase the operation complexity.
In order to solve the above problems, there is a need for studying other cutting processes.
Laser cutting technique has become a proven industrial processing technique. In addition to laser cutting for metals, a new development may be made in laser cutting for ceramic. GOS ceramic scintillator is not fully transparent, and its light transmittance is not too high (for a thickness of 1.5 mm, its light transmittance is less than 50%). Therefore, the laser cutting technique can be applied to cut low light-transmittance objects, for example GOS ceramic scintillator array. Herein, the feature that “transmittance” or “light transmittance” is less than 50% indicates “transmittance for visible light wave band”, and the used laser wavelength is associated with the transmittance. That is to say, for the wavelength of employed laser, the ceramic scintillator (an object to be processed) should have a low transmittance (i.e., a high absorbance), which is well known in the art of laser processing. Furthermore, the laser cutting process has a high processing speed, can easily adjust the widths of cuts, and can adjust the quality of cut (for example, surface roughness of the cut) by adjusting the pulse repetition frequency of laser and the moving speed of the working platform on which the scintillator is placed. Therefore, the laser cutting technique is a promising cutting process of GOS scintillator. However, there are several problems in the laser cutting for GOS scintillator. For example, hidden cracks may arise when a GOS scintillator is irradiated by laser beams of high energy. If a cut is not well protected during the cutting process, the cut will be blackened and thus loss of scintillation light on end surfaces of the cut will be increased, which will adversely affect light output of the scintillator. In addition, if the slags are not promptly removed from surfaces of the cuts, the cuts will be blocked, and the non-through cuts will affect the subsequent filling of the light-reflective synthetic-resin cement.